It began sometime in late 1998 or early 1999 when Nott was driving on the M4. His mobile phone signal went down and, after pulling off at a motorway service station, he called his provider, Vodafone.

He explained his urgent need to access his voicemail messages and was informed that it wasn't a problem. He could pick up messages from another phone, whether it be a landline or mobile.

To his amazement he was told a fail-safe technique that involved tapping in a default pin number. "I was gobsmacked," he writes. "It was so easy."

He says he "spent the next couple of months having fun and games with my mates' phones, work colleagues' phones and so on."

But he also realised it was a serious matter too. People should be made aware of the vulnerabilities of their mobile phone messages.

He complained first to Vodafone, but says the company appeared unworried. Then he did all he could to raise the alarm.

He says he wrote to MI5 and to the department of trade and industry. He also called the Daily Mirror, hoping to give the paper a scoop.

He says that, over a period of several days, he spoke to a woman on the Mirror newsdesk, who was excited by the story. (He knows her identity but says he cannot name her "for legal reasons").

He claims the woman said the Mirror was planning to run a piece about how celebrities' phones could be hacked. But the the story did not appear and he says he was paid £100.

So he contacted the Mirror's major rival, The Sun, and met the paper's then consumer affairs correspondent, Paul Crosbie, to tell him his story.

Crosbie, who now works in PR, confirmed Nott's account of his visit to the BBC, saying: "I did meet Steven and was surprised by what he'd discovered.

"I wrote up what I thought was a very good story, but it never ran."

Nott did eventually manage to raise his concerns in an interview with BBC radio's 5 Live, which alerted his local paper. Nott, who lives in Cwmbran, finally saw his story published in print in the South Wales Argus in October 1999.

The "exclusive" by reporter Rob Skellon told readers how the "horrified Vodafone subscriber" had discovered that anyone could "access his answer phone service and listen to his private messages."

Nott's quotes at the time were eerily prescient. He told the Argus:

"Vodafone has millions of users, and many of them will be MPs and high-ranking government officials, people with highly sensitive information at their fingertips.

"I thought it important that the intelligence service should know about this.

"Unauthorised accessing of someone's message service is on a par with tampering with their mail."

With hacking revelations finally becoming big news earlier this year, Nott wrote to John Prescott and in March this year, Prescott wrote back to Nott to say he was passing his information to the Met police.

Nott says he was also called as a witness in one of the civil actions against the News of the World publisher, News International, and its private investigator Glenn Mulcaire.

Nott has written on his blog: "I always wanted the public to know from the very outset. I tried my hardest to get the press to take the story and failed."

Nott does not claim to be the first person to discover how easy it was to hack a person's mobile phone.

But Nott does believe he was the first to try to bring it to the attention of the wider public by telling journalists about it.

He says that, of course, he didn't anticipate that journalists would use the technique themselves, adding: "I'm appalled because I really do seriously think I may have inadvertently started this in the early days."

News International and Trinity Mirror have both declined to comment on the claims.